Two-dimensional simulation and modal analysis of hollow electron beams for controlled halo collimation

摘要

The existing high-energy particle accelerators have used collimator system consisting of thin tungsten plates to remove beam halos. In this configuration, the minimum distance between the collimator and the beam axis is limited by instantaneous loss rates, radiation damage, and the electromagnetic impedance of the device. To reduce these effects, a collimator system making use of a hollow electron beam was recently proposed and also successfully tested in the Fermilab Tevatron [1]. If the hollow electron beam is to be operated with much higher beam currents, the so-called diocotron instability can be a major limiting factor. In this study, we investigate detailed characteristics of the diocotron instability using a two-dimensional particle-in-cell simulation and compare the observed growth rates with the theory based on azimuthal mode analysis. Presented are comparisons between measurements and simulations, validity of the scaling law, and the effects of conducting wall and beam offset.